Environmental Geochemistry And Potential Ecological Risk Of The Second Songhua River

Presently a variety of scientific researches targeted on river basin due to its characteristics of huge drainage area, rich fresh water resources, fertile land, large population, dense towns, the more developed industrial and agricultural production and others, has gradually become the core of the earth's surface system investigation The Second Songhua River as the largest river in Jilin province whose total area of the basins is 7.3 million square kilometers, accounting for 38.2% of the total area of the province, is the major commodity grain production base and industrial concentration in the northeast of China. In recent years, with the rapid economic development in the Second Songhua River, water environment issues become prominent increasingly. The water environment characteristics and the potential ecological risks of the Second Songhua River were researched in this paper mainly from the perspective of environmental geochemistry.Totally 38 water samples and 117 sediment samples in the Second Songhua River and its major tributaries were collected for this research. The Cr, Cu, Pb and Zn contents in the samples were measured by X-ray fluorescence spectrometer (TW2440), and Cd content was available by atomic absorption spectrophotometer with a graphite furnace (M6). The As and Hg contents were determined by atomic fluorescence spectrophotometer (AFS-230E). The test equipment for phthalates, PAHs, and benzene class of organic pollutants in water and sediment is the Agilent 6890/5973N GC-MS. The chromatogram was DB-5MS and 30m×0.25mm×0.25μm with the temperature 250℃of vaporization chamber inlet and the column flow 1ml/min. The heating procedure was keeping 2 minutes in 50℃and then heating to 200℃which maintained 10 minutes by 5℃/ min rate, and rising up to 250℃maintaining 30min by 10℃/ min rate in the end with the splitless injector mode and 2 minutes solvent delay time. The electron multiplier voltage was 2282v; the quadrupole temperature was 150℃with the MS scan range of 15 ~ 400u and the EI ion source temperature of 230℃. National standard material was used to control the quality in the analysis and the results accorded to the quality control requirements. The statistical characteristics of heavy metals concentrations in water from the Second Songhua River suggest that whether it was wet or dry season period, the average levels of heavy metals in water were low and far less thanⅢ-class water quality standard in national surface water environmental quality standards, so generally it was consistent with the water quality requirements as drinking water source. The contents in water of As, Cd, Cr, and Hg in the dry season were all higher than in the wet period, while the Cu, Pb, and Zn were on the contrary, that mean the contents in water were lower in the dry season than in the wet period.The heavy metals contents in sediments were much higher than in water in the Second Songhua River but were still at a relatively low level compared to other major rivers in China. The highest concentrations values of the studied seven kinds of heavy metals were all in the Second Songhua River middle reaches in where the values were significantly higher than in other reaches; in the source area of this river, except Hg content in sediments was slightly higher in Erdaobaihe river than in Toudaobaihe river, the contents of remaining heavy metals were higher in Toudaobaihe river; in the two main tributaries named Huifa river and Jiaohe river in upper reaches, the contents of As, Pb, and Zn in sediments were higher in Jiaohe river, while the Cd, Cr, Cu, and Hg were opposite. The heavy metals contents in sediments and in water basically had the same change characteristics along the way in the middle and lower reaches, that the contents in sediments were much higher in urban river than in non-urban river.It showed that water body was clearly affected by the urban industrial activities.The two main kinds of phthalates in water from the Second Songhua River were DBP mean 717.24μg /l and DEHP mean 370.02μg/l, whose averages have exceeded China's standard limits for surface water (3μg/l for DBP, 8μg/l for DEHP). The averages of naphthalene, phenanthrene, benzo [b] fluoranthene, benzo [k] fluoranthene and benzo [a] pyrene in water were all at a comparative low level, and in particular benzo [b] fluoranthene, benzo [k] fluoranthene and Benzo [a] pyrene were not detected in water at all. Also the averages of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene in water were comparative low. The two main kinds of phthalate esters in sediments were DBP and DEHP that was consistent with the detection of PAEs in water; the contents both of total and various components of the phthalate esters had a certain degree of variation in distribution along the way, presenting increase firstly and then decrease, and the maximum points in contents all located in the middle reaches of urban river in Jilin City. The total amount of polycyclic aromatic hydrocarbons in different samples ranged from 106.91 to 20330.95μg/kg with an average of 3788.56μg/kg. The contents of a variety of polycyclic aromatic hydrocarbons and total PAHs in sediments were higher in urban river than in non-urban river. The total detection rate of benzenes in sediments was 88%. Including detection rates of benzene, toluene and ethylbenzene were highest up to 100%, and the lowest of o-xylene was only 50%. Polycyclic aromatic hydrocarbons and benzene contents basically had the same variation as phthalate esters along the way.The potential ecological risk evaluation of heavy metals pollution in sediments from the Second Songhua River were finished in this paper by use of the potential ecological risk index method proposed by Swedish scholar Hakanson. The results showed that potential ecological risks of heavy metal elements in the Second Songhua River sediments were at a general low level relatively mainly Hg-based ecological risk. But the heavy metal elements in sediments from the Second Songhua River middle and lower reaches showed moderate to strong ecological risk, to which should be paid more vigilance. The ecological risk assessment for polycyclic aromatic hydrocarbons in sediments was done by use of a method proposed by Long and other U.S. scholars, which is used to evaluate the ecological risk effects of organic pollutants by low value(ERL, probability of biological harmful effects less than 10%) and median value(ERM, probability of biological harmful effects more than 50%) in the effect range of ecological risk. The results showed that polycyclic aromatic hydrocarbons in the middle and lower reaches of the Second Songhua River which belonged to higher ecological risks river, might have a certain negative effects on biology. And the results of ecological risk assessment using the quotient method for phthalic acid esters in water showed that the water phthalate DEHP in 62.5% of samples have a low potential ecological risk to algae.